Martin Marietta Spacemaster

The Martin Marietta Spacemaster was a proposed design for what became the Space Shuttle, put forward by Martin Marietta and evaluated in 1967 before it was rejected. It combined an orbiter derived from the company X-24 lifting body with an unusual catamaran style booster of two parallel halves. During launch and ascent the orbiter would sit in a recess between them, and the booster would carry 14 engines in two clusters of seven at the bottom of the halves. Unlike the final Space Shuttle there would have been no external tank, and connecting struts would join the two booster halves and hold the orbiter. Martin Marietta went on to build the Space Shuttle external tank instead, and a model of the Spacemaster is held by the Smithsonian National Air and Space Museum.